Electrofusion joint and hot water supply header using the same

ABSTRACT

The improved electrofusion joint and header for supplying hot water that perform satisfactorily at elevated temperatures as evidenced by high heat resistance, that exhibit good sealing property and that can be handled efficiently in mounting and various other operations have a crosslinked thermoplastic resin layer and at least one joining portion which comprises a non-crosslinked thermoplastic resin layer that is formed a as an integral part of said crosslinked thermoplastic resin layer in the area where it contacts a tubular member to be joined, and a heating electric wire provided either within or on the outer or inner surface of said non-crosslinked thermoplastic resin layer. Such electrofusion joint and header are applicable to any part of a piping system for supplying hot water and they will withstand use for a prolonged period.

BACKGROUND OF THE INVENTION

The present invention relates to an electrofusion joint with whichmembers such as polyolefin pipes, in particular, conduits for supplyinghot water are joined or connected either to themselves or to the lateralside of other conduits. The present invention also relates to anelectrofusion joint fitted with a connecting member for establishingconnection to terminals such as nozzles on a conduit header. The presentinvention further relates to a header for distributing hot water from aheat source providing apparatus such as a hot water supplier to morethan one site of use.

Pipes made of crosslinked polyolefins such as silane-crosslinkedpolyethylene are used as conduits for supplying hot water. Crosslinkedpolyolefins perform satisfactorily at elevated temperatures as evidencedby high heat resistance and good high-temperature creep characteristicand have a shape-retaining capability. However, unlike non-crosslinkedpolyolefins, crosslinked polyolefins cannot be fused to members to bejoined. Hence, electrofusion joints used to connect non-crosslinkedpolyolefin pipes are not applicable to crosslinked polyolefin pipes. Itis also impossible to form electrofusion joints using crosslinkedpolyolefins.

Therefore, crosslinked polyolefin pipes are currently joined by means ofmechanical couplings, or joints that rely upon mechanical couplings areproduced from crosslinked polyolefins. However, mechanical joints usedin connecting hot water pipes which require high strength to withstandhigh operating pressures involve a complicated structure and cannot behandled efficiently in piping work. Further, compressive sealingperformed with these mechanical joints causes the disadvantage thattheir performance will decrease with time as exemplified bydeterioration in the reliability of sealing due to creeping in pipes orstress relaxation of pipes and sealants.

Further, if thin-walled resin pipes are connected by conventionalelectrofusion joints, the joined portions will thermally deform andbulge inwardly to restrict the fluid passage.

An electrofusion joint formed of a thermoplastic resin is known that isprovided with a fine orifice in the body of the joint, through which theresin that has become molten when a member of interest is joined byfusion will come out to provide a measure for checking whether saidmember has completely fused to the joint (see, for example, UnexaminedPublished Japanese Patent Application No. 61-62696). However, beingformed of a kind of thermoplastic resin, this prior art electrofusionjoint has the disadvantage that the molten resin coming out of theorifice has the same color as the surrounding resin of which the jointis formed and that extrusion of this resin is difficult to identify.Thus, the time at which fusion has been completed cannot be detectedprecisely.

Further, connecting terminals such as nozzles on a conduit header areusually metallic and it is difficult to connect them to crosslinkedthermoplastic resin pipes.

FIG. 23 is a diagram showing a piping system for supplying hot water.Shown by 81 in the diagram is a header by which hot water from a heatsource providing apparatus 82 such as a hot water supplier isdistributed to a faucet 83 in the kitchen, a faucet 84 in the lavatory,a faucet 85 in the bathroom, and other outlets. The heat sourceproviding apparatus 82 receives water from a supply pipe 86, heats it byburning the gas supplied through a gas pipe 87, and supplies the heatedwater through a hot water main 88 to the header 81.

Header 81 is shaped of a metal in hollow form and has a singlereceptacle 91 on the inlet side and a plurality of receptacles of samediameter 92a, 92b, 92c, 92d, . . . on the outlet side. The receptacle 91on the inlet side is connected to the hot water main 88 by fasteningmeans such as screws, whereas the receptacles 92a, 92b, 92c, 92d, . . .on the outlet side are connected to branch pipes 93a, 93b, 93c, 93d, . .. by fastening means such as screws. The branch pipes 93a, . . . havesuch bore diameters that faucets 83, 84, 85, are supplied with hot waterin the necessary flow rates that correspond to the capacities of therespective faucets.

The conventional header 81 has had several problems on account of thefact that it is formed of metal. First, it is liable to corrosion and isheavy. Second, it is difficult to connect to plastic pipes and is notsuitable for large-scale production.

Further, the header 81 fitted with a plurality of receptacles of samediameter 92a, . . . on the outlet side has to be connected to branchpipes 93a, . . . of smaller diameter by means of reducers and this hasbeen another factor that makes the header unsuitable for large-scaleproduction.

SUMMARY OF THE INVENTION

Therefore, a first object of the present invention is to provide anelectrofusion joint that uses a crosslinked thermoplastic resin such asa crosslinked polyolefin to provide enhanced heat resistance, that yetallows for fusion to insure enhanced sealing property and that can behandled with efficiency.

A second object of the present invention is to provide an electrofusionjoint that has not only the features described above but also acapability for fusion without causing thermal deformation of the memberto be joined.

A third object of the present invention is to provide an electrofusionjoint that uses a crosslinked thermoplastic resin to provide enhancedheat resistance, that enables the operator to easily check thecompletion of joint fusion, thereby insuring that member to be joined iscompletely fused to the joint to provide enhanced sealing performance,and that can be handled with efficiency.

A fourth object of the present invention is to provide an electrofusionjoint fitted with a connecting member that uses a crosslinkedthermoplastic resin to provide enhanced heat resistance, that yet allowsfor fusion to insure enhanced sealing performance, that enablescrosslinked thermoplastic resin pipes to be easily joined to connectingterminals such as nozzles on a conduit header, and that can be handledwith efficiency.

A fifth object of the present invention is to provide an electrofusionjoint fitted with a connecting member that has not only the featuresdescribed above but also a capability for fusion without causing thermaldeformation of the member to be joined.

A sixth object of the present invention is to provide an electrofusionjoint that uses a crosslinked thermoplastic resin to provide enhancedheat resistance, that yet allows for fusion to insure enhanced sealingperformance, that can be connected to the lateral side of a conduit atwill, and that can be handled with efficiency.

A seventh object of the present invention is to provide a header forsupplying hot water that is lightweight and corrosion-resistant, thatcan be easily connected to plastic pipes, and that is suitable forlarge-scale production.

A eighth object of the present invention is to provide a header forsupplying hot water that is lightweight and corrosion-resistant, thatcan be easily connected to plastic pipes having different borediameters, and that is suitable for large-scale production.

The above-stated objects of the present invention can be attained by afirst embodiment which provides an electrofusion joint having at leastone joining portion which comprises a crosslinked thermoplastic resinlayer, a non-crosslinked thermoplastic resin layer that is formed as anintegral part of said crosslinked thermoplastic resin layer in the areawhere it contacts a tubular member to be joined, and heating electricwire provided either within or on the outer or inner surface of saidnon-crosslinked thermoplastic resin layer.

According to a second embodiment of the present invention, said joiningportion further includes a support of the member to be joined which isprovided in such a way as to form a groove into which the end of saidmember to be joined is to be inserted.

According to a third embodiment of the present invention, saidcrosslinked thermoplastic resin layer and the non-crosslinkedthermoplastic resin layer on the inner surface thereof have differentcolors, which crosslinked thermoplastic resin layer has a fine orificethat extends from its outer surface to a point close to the boundarybetween said crosslinked thermoplastic resin layer and saidnon-crosslinked thermoplastic resin layer.

According to a fourth embodiment of the present invention, saidelectrofusion joint further includes a connecting portion comprising atubular crosslinked thermoplastic resin layer and a connecting memberthat is secured to said crosslinked thermoplastic resin layer by beinginserted inwardly or outwardly of the same.

According to a fifth embodiment of the present invention, said joiningportion further includes a support of the member to be joined which isprovided in such a way as to form a groove into which said member to bejoined is to be inserted.

According to a sixth embodiment of the present invention, said joiningportion is shaped like a saddle and is a first connecting portion havinga second connecting portion on its top.

According to a seventh embodiment of the present invention, there isprovided a header for distributing hot water from a heat sourceproviding apparatus, which header comprises a header body shaped of acrosslinked thermoplastic resin in a hollow form, a receptacle providedon the inlet side of said header body and at least one receptacle on theoutlet side, at least part of these receptacles having a tubular layerformed of a crosslinked thermoplastic resin as an integral part of saidheader body, a non-crosslinked thermoplastic resin layer superposed asan integral part of said crosslinked thermoplastic resin layer in thearea where it is joined to a pipe to be connected, and a heatingelectric wire provided either within or on the outer or inner surface ofsaid non-crosslinked thermoplastic resin layer.

According to an eighth embodiment of the present invention, there isprovided a header for distributing hot water from a heat sourceproviding apparatus, which header comprises a header body shaped of acrosslinked thermoplastic resin in a hollow from, a receptacle providedon the inlet side of said header body, a plurality of receptacles on theoutlet side, each of said receptacles on the outlet side having atubular layer formed of a crosslinked thermoplastic resin as an integralpart of said header body in such a way that said tubular resin layer hasa bore diameter sufficient to admit the flow rate of hot waterdistributed to each receptacle.

In the first embodiment, it is preferred that the crosslinkedthermoplastic resin layer in the electrofusion joint is a crosslinkedpolyolefin layer, with the non-crosslinked thermoplastic resin layerbeing a non-crosslinked polyolefin layer.

It is also preferred that the non-crosslinked thermoplastic resin layerin the electrofusion joint is formed on the inner surface of thecrosslinked thermoplastic resin layer so that said non-crosslinkedthermoplastic resin layer will contact the circumference of the tubularmember to be joined.

In yet another preferred embodiment, the joining portion is shaped likea saddle.

In the second embodiment, it is preferred that the support of the memberto be joined is formed as an integral part of said crosslinkedthermoplastic resin layer or said non-crosslinked thermoplastic resinlayer.

In the fourth embodiment, it is preferred that the crosslinkedthermoplastic resin layer in the connecting portion is adhered to theconnecting member by means of a modified thermoplastic resin.

In the fifth embodiment, it is preferred that the support of the memberto be joined is formed as an integral part of the connecting member.

In the sixth embodiment, it is preferred that the second connectingportion is the joining portion.

It is also preferred that second connecting portion has a crosslinkedthermoplastic resin layer and a connecting member secured to thecrosslinked thermoplastic resin layer as an integral part thereof.

It is also preferred that the second connecting portion has a tubularcrosslinked thermoplastic resin layer and a non-crosslinkedthermoplastic resin layer superposed on the circumference of saidcrosslinked thermoplastic resin layer as an integral part thereof.

In the eighth embodiment, it is preferred that at least part of thereceptacles on the inlet and outlet sides of the header body has anon-crosslinked thermoplastic resin layer superposed as an integral partof said crosslinked thermoplastic resin layer in the area where it isjoined to a pipe to be connected, and a heating electric wire providedeither within or on the outer or inner surface of said non-crosslinkedthermoplastic resin layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 are partial fragmentary front views of three examplesof an electrofusion joint according to the first embodiment of thepresent invention;

FIGS. 4 and 5 are of two examples of an electrofusion joint according tothe second embodiment of the present invention;

FIGS. 6 is a partial fragmentary front view of an example of anelectrofusion joint according to the third embodiment of the presentinvention;

FIGS. 7, 8 and 9 are cross sections of three examples of anelectrofusion joint equipped with a connecting member according to thefourth embodiment of the present invention;

FIGS. 10, 11 and 12 are cross sections of three examples of anelectrofusion joint equipped with a connecting member according to thefifth embodiment of the present invention;

FIGS. 13 is a front view of an illustrative electrofusion jointaccording to the sixth embodiment of the present invention;

FIGS. 14 is a cross section taken on line A--A of FIG. 13;

FIG. 15 is a bottom view of the electrofusion joint shown in FIG. 13;

FIG. 16 is a partial fragmentary front view of the same electrofusionjoint that includes a cross section taken on line B--B of FIG. 14 andwhich illustrates how the joint is mounted on a member to be joined;

FIGS. 17 and 18 are partial fragmentary front views showing how twoother examples of the electrofusion joint according to the sixthembodiment of the present invention are mounted on the member to bejoined;

FIGS. 19 and 20 are partial fragmentary front views of two examples of aheader for supplying hot water according to the seventh embodiment ofthe present invention;

FIGS. 21 and 22 are partial fragmentary front views of two examples of aheader for supplying hot water according to the eighth embodiment of thepresent invention;

FIG. 23 is a diagram showing an illustrative piping system for supplyinghot water.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below.

In the electrofusion joint and the header for supplying hot water of thepresent invention, the crosslinked thermoplastic resin layer is adjacentto and integral with the non-crosslinked thermoplastic resin layer.Crosslinked thermoplastic resins such as crosslinked polyolefins do notfuse, so even if a crosslinked thermoplastic resin and non-crosslinkedthermoplastic resin such as a non-crosslinked polyolefin are shaped byextrusion molding, injection molding or some other methods, the layersof the respective resins will not fuse together but separate from eachother. Instead, if a crosslinkable thermoplastic resin yet to becrosslinked and a non-crosslinked thermoplastic resin are thermoformedinto an integral unit and with the crosslinkable thermoplastic resinbeing subsequently crosslinked, a laminate which is an integral unit ofthe crosslinked thermoplastic resin and the non-crosslinkedthermoplastic resin will be obtained. The electrofusion joint of thepresent invention uses this laminate in which the crosslinkedthermoplastic resin layer unit is present.

The crosslinked thermoplastic resin has a steric structure created bycrosslinking between the molecules of a thermoplastic resin.Crosslinking may be achieved with the aid of a crosslinking agent as inthe case of silane-crosslinked thermoplastic resins anddivinylbenzene-crosslinked thermoplastic resins. Alternatively, directcrosslinking may be effected by such means as organic peroxides andradiation.

The crosslinkable thermoplastic resins yet to be crosslinked accordingto the present invention comprise polyolefins which have a crosslinkingability created by reacting polyolefins with the crosslinking agent,such as a silane compound, but are not yet crosslinked. Theelectrofusion joint and the header for distributing hot water from aheat source providing apparatus are fabricated by thermoforming such thecrosslinkable thermoplastic resin layer yet to be crosslinked and thenon-crosslinked thermoplastic resin layer into an integral unit.Thereafter, the crosslinkable thermoplastic resin layer yet to becrosslinked is crosslinked by including crosslinking reaction by meansof a hot water treatment and the like.

The non-crosslinked thermoplastic resin is selected from amongnon-crosslinkable thermoplastic resins such as polyolefins whichgenerally are used as thermoplastic resins.

Polyolefins are preferably used as thermoplastic resins of thecrosslinkable thermoplastic resin yet to be crosslinked and thenon-crosslinked thermoplastic resin in the present invention andillustrative polyolefins include homo- and copolymers of α-olefinshaving 2-20, preferably 2-12, carbon atoms. Preferred α-olefins includeethylene, propylene, butene-1 and 4-methylpentene-1.

The present invention is hereunder described in greater detail withreference to the preferred embodiments shown in accompanying drawings.To begin with, the first embodiment of the present invention isdescribed below with reference to FIGS. 1 to 3.

The electrofusion joint of the present invention is such that at leastone its joining portion is fabricated by the following procedure: thenon-crosslinked thermoplastic resin layer having a heating electric wireeither within or on its outer or inner surface or having said wire woundonto its surface is inserted into an injection mold cavity; acrosslinkable thermoplastic resin is injected and laminated on saidnon-crosslinked thermoplastic resin layer; thereafter, the crosslinkablethermoplastic resin layer is crosslinked to form the crosslinkedthermoplastic resin layer.

The thus fabricated electrofusion joint is mounted on the joining partsof members to be joined such as thermoplastic resin (e.g. polyolefin)tubes in such a way that the non-crosslinked thermoplastic resin layerwill contact said members. When an electric current is applied to theelectric wire, the non-crosslinked thermoplastic resin layer will meltand fuses to the member to become an integral part of the latter.

Members to be joined by the electrofusion joint of the present inventionare preferably such that the surface layer or the entire portion is madeof a thermoplastic resin, in particular, a miscible thermoplastic resin.Members made of non-crosslinked thermoplastic resins such as polyolefinswill exhibit particularly good fusing ability.

Examples of the first embodiment of the present invention arespecifically described below with reference to drawings. FIGS. 1, 2 and3 are front views of electrofusion joints, with their right half shownin cross section, according to three different examples of the firstembodiment. In each of these drawing, the electrofusion joint 10 has atubular crosslinked polyolefin layer 12 forming the main body of thejoint, and two joining portions that comprise a non-crosslinkedpolyolefin layer 13 formed as an integral part of said crosslinkedpolyolefin layer 12 on the inner side thereof at each of the positionswhere it contacts two members to be joined 15 and 16, and a heatingelectric wire 14 provided either within or on the outer or inner surfaceof said non-crosslinked polyolefin layer 13.

The members 15 and 16 are pipes having a layer of a thermoplastic resinsuch as polyethylene. While they may be totally made of fusiblethermoplastic resin, pipes formed of a heat-resistant material such as acrosslinked polyolefin should be coated with a fusible thermoplasticresin on the outer surface. The crosslinked polyolefin layer 12 has atubular structure that surrounds the entire circumference of the members15 and 16 in their mating portion 17 and nearby areas. Thenon-crosslinked polyolefin layer 13 is superposed on the inner surfaceof the crosslinked polyolefin layer 12 in areas at opposite ends thereofin its longitudinal direction that correspond to the members 15 and 16.The heating electric wire 14 is provided either within thenon-crosslinked polyolefin layer 13 as shown in FIG. 1, or in its outersurface as shown in FIG. 2, or in its inner surface as shown in FIG. 3.

The electric wire 14 is fitted with leads (not shown) so that it can beconnected to an external power source also not shown.

The electrofusion joint 10 having the construction described above isfabricated by the following procedure: with the heating electric wire 14buried in or wound around the non-crosslinked polyolefin layer 13, acrosslinkable polyolefin layer containing a crosslinking agent, acrosslinking aid, a catalyst, etc. in a polyolefin is laminated oversaid non-crosslinked polyolefin layer 13 to form an integral unit, andthereafter, said crosslinkable polyolefin layer is crosslinked to formthe crosslinked polyolefin layer 12.

The thus fabricated electrofusion joint 10 is mounted in the matingportion 17 of members 15 and 16 and nearby areas in such a way that thenon-crosslinked polyolefin layer 13 will contact said members 15 and 16.When an electric current is applied to the electric wire 14 from anexternal power source connected by leads (not shown), thenon-crosslinked polyolefin layer 13 will melt and fuses to the members15 and 16 to become an integral part of the latter.

In the electrofusion joint 10 of the present invention, the tubularcrosslinked polyolefin layer 12 forming the main body of the joint isresponsible for imparting heat resistance to the joint. Hence, the jointis capable of retaining its own shape in an effective way even if it isused to join hot water supply pipes. Further, the non-crosslinkedpolyolefin layer 13 which is an integral part of the crosslinkedpolyolefin layer 12 fuses to the members 15 and 16 to become an integralpart thereof. Hence, the joint 10 has good sealing property which ismaintained for a prolonged period even if it is used to join hot waterpipes.

The shapes and structures of the crosslinked polyolefin layer 12 and thenon-crosslinked polyolefin layer 13 are not limited to those shown inFIGS. 1-3 and various modifications are possible. In the examples shownin these drawings, members 15 and 16 meet directly each other in themating portion 17 inside the electrofusion joint 10. If desired, themembers 15 and 16 may be caused to meet a projection provided on thecrosslinked polyolefin layer 12. In the examples shown in FIGS. 1-3, thenon-crosslinked polyolefin layer 13 having the heating electric wire 14is provided independently on either side of the mating portion 17 in theareas of contact with the members 15 and 16. Alternatively, a continuoussingle layer of non-crosslinked polyolefin may be provided to cover theareas of contact with the members 15 and 16 if the electric wire 14 isto be provided on either the outer or inner surface of thenon-crosslinked polyolefin layer 13, it may be wound around saidnon-crosslinked polyolefin layer 13 or the members 15 and 16.

In the examples shown in FIGS. 1-3, the electrofusion joint 10 connectstwo members 15 and 16 in a straight line with their ends meeting eachother. The present invention is not limited to these examples alone andmay embrace joints having more than one portion for connecting membersto be joined such as an elbow joint, a T-joint and a cross joint. Ablind joint closed at one end is also included within the presentinvention. If joints having two or more connecting portions are used, atleast one of the connecting portions must be an electrofusion joiningportion that comprises the crosslinked polyolefin layer 12 and thenon-crosslinked polyolefin layer 13 that is integral with saidcrosslinked polyolefin layer 12 and which has the heating electric wire14. Thus, the other connecting portions may have a connecting membersuch as a screw secured thereto. The main body of the joint need not betotally formed of the crosslinked polyolefin layer 12 but from theviewpoint of molding, it is preferred that the main body of the joint istotally formed of the crosslinked polyolefin layer 12.

In the examples described above, the non-crosslinked polyolefin layerhaving the heating electric wire in the joining portion is formed on theinner surface of the crosslinked polyolefin layer so that it willcontact the circumference of the members to be joined. However, thepresent invention is not limited to this case alone and thenon-crosslinked polyolefin layer may be formed on the outer surface ofthe cross-linked polyolefin layer in such a way that it will join theinside surfaces or ends of the members to be joined.

In the examples described above, the electrofusion joint has a tubularjoining portion for joining the ends of members to be joined. Thepresent invention is not limited to this case alone and the joiningportion may be shaped like a saddle so that it is capable of joining tothe lateral side of a member to be joined.

As described in detail on the foregoing pages, the electrofusion jointaccording to the first embodiment of the present invention has a joiningportion comprising a non-crosslinked thermoplastic resin layer that isformed as an integral part of a crosslinked thermoplastic resin layerand which has a heating electric wire provided either within or on itsouter or inner surface. Hence, this joint performs satisfactorily atelevated temperatures as evidenced by high heat resistance and exhibitsgood sealing property. In addition this joint can be handled efficientlyin mounting and various other operations.

The second embodiment of the present invention is described below withreference to FIGS. 4 and 5.

The electrofusion joint according to the second embodiment of thepresent invention has not only the constituent elements described abovein connection with the first embodiment but also a support of the memberto be joined which is provided in the joining portion to form a grooveinto which the end of said member to be joined is to be inserted. Thesupport is preferably provided on the side that faces thenon-crosslinked thermoplastic layer. The groove into which the member tobe joined is to be inserted is formed in such a way that it opens at theconnecting end of the electrofusion joint. The support of the member tobe joined is desirably formed as an integral part of the crosslinkedthermoplastic resin layer by being made of a crosslinked ornon-crosslinked thermoplastic resin. If desired, the support may be madeof other materials.

As in the first embodiment, the electrofusion joint according to thesecond embodiment is fabricated by crosslinking a cross-linkablethermoplastic resin that has been shaped as a laminated integral part ofa non-crosslinked thermoplastic resin having a heating electric wireburied in or wound on it. In this second embodiment, the support of themember to be joined may be formed as an integral part of either thecrosslinkable thermoplastic resin which is to form the crosslinkedthermoplastic resin layer or the non-crosslinked thermoplastic resin.

The thus fabricated electrofusion joint is used in the following manner:a member to be joined such as a thermoplastic resin tube is inserted atone end into the groove which is open at the connecting end of thejoint; the member is mounted in such a way that it contacts thenon-crosslinked thermoplastic resin layer and is supported by saidsupport; when an electric current is applied to the electric wire, thenon-crosslinked thermoplastic resin layer will melt and fuses to themember of interest to become an integral part of the latter. As thenon-crosslinked thermoplastic resin layer melts, the member to be joinedsuch as a thermoplastic resin tube will soften but will not deform sinceits inner surface is supported by its support.

Examples of the second embodiment of the present invention are describedbelow in a specific way with reference to drawings. FIGS. 4 and 5 arecross sections of two different examples of an electrofusion jointaccording to the second embodiment of the present invention. Except forthe groove into which the member to be joined is to be inserted and thesupport of said member, the electrofusion joints shown in FIGS. 4 and 5have the same construction as the electrofusion joint 10 shown in FIG. 1and hence, the same components are identified by like numerals and willnot be described in detail.

Each of the electrofusion joints 20 and 21 shown in FIGS. 4 and 5,respectively, has a crosslinked polyolefin layer 12 forming the mainbody of the joint, non-crosslinked polyolefin layers 13 and heatingelectric wires 14. Further, these joints have supports 23 for members 15and 16 to be joined which are provided in such a way as to form grooves22 inwardly of the non-crosslinked polyolefin layers 13 into which themembers 15 and 16 can be inserted at their ends. In the examples shown,the joining portion consisting of non-crosslinked polyolefin layer 13,heating electric wire 14, groove 22 and support 23 is provided on eachside of the electrofusion joint 20 or 21.

In the electrofusion joint 20 shown in FIG. 4, the supports 23 are madeof a crosslinked polyolefin and extend from the center of thecrosslinked polyolefin layer 12 as an integral part thereof in such away as to form grooves 22 between those supports and the non-crosslinkedpolyolefin layers 13.

The electrofusion joint 20 may be fabricated by the process described inconnection with the electrofusion joint 10, except that the injectionmold cavity used must be so designed as to permit the shaping of grooves22 and supports 23.

After fabricating the electrofusion joint 20 as described above, themembers to be joined 15 and 16 such as polyolefin tubes are inserted atone end into grooves 22 on opposite sides of the joint 20 and mounted insuch a way that they contact the non-crosslinked polyolefin layers 13and are supported by the supports 23. Thereafter, an electric current isapplied to the electric wires 14, whereupon the non-crosslinkedpolyolefin layers 13 are melted and fuse to become an integral part ofthe members 15 and 16.

As the non-crosslinked polyolefin layers 13 melt, the members 15 and 16which are made of thermoplastic resin will soften but will not deformsince their inner surfaces are supported by the supports 23. Thus, thefluid passage of each of the members 15 and 16 will not become narrowerbut maintains a cross-sectional area substantially the same as beforethese members were joined.

As in the case of the electrofusion joint 21 shown in FIG. 5, the secondembodiment of the present invention may be such that the supports 23 areformed as integral parts of the non-crosslinked polyolefin layers 13 bybeing made of a non-crosslinked polyolefin.

The shapes and structures of the crosslinked polyolefin layer 12,non-crosslinked polyolefin layers 13, heating electric wires 14,supports 23, etc. are not limited to those shown in FIGS. 4 and 5 andvarious modifications are possible.

It should be particularly noted that in the second embodiment of thepresent invention, the portions to be joined by the non-crosslinkedpolyolefin layers 13 having heating electric wires 14 are not limited tothe circumferences of the members 15 and 16 and they may be the innerand outer circumferences of these members including their ends or theinner circumferences of such members.

It should also be noted that the electrofusion joint according to thesecond embodiment need only have at least one joining portion containingthe supports 23 which are provided in such a way as to form grooves 22into which the members 15 and 16 are to be inserted. The number of suchjoining portions and their shape and structure, as well as the shape ofthe main body of the joint, and even the structure of other joiningportions are not limited in any particular way. Further, the joint mayor may not have a connecting member.

As described above in detail, the electrofusion joint of the secondembodiment of the present invention has a joining portion that comprisesheating electric wires provided either within or on the outer or innersurface of non-crosslinked thermoplastic resin layers which are integralparts of a crosslinked thermoplastic resin layer, and a support of amember to be joined that is provided in such a way as to form a grooveinto which said member is to be inserted. Because of this construction,the joint performs satisfactorily at elevated temperatures as evidencedby high heat resistance and exhibits good sealing property. In addition,this joint is capable of connecting members without causing theirdeformation and it can be handled efficiently in mounting and variousother operations.

The third embodiment of the present invention is described below withreference to FIG. 6. The electrofusion joint according to the thirdembodiment of the present invention is the same as the one of the firstor second embodiment except that the outer crosslinked thermoplasticresin layer and the inner non-crosslinked thermoplastic resin layer havedifferent colors, which crosslinked thermoplastic resin layer has a fineorifice that extends from its outer surface to a point close to theboundary between said crosslinked thermoplastic resin layer and theinner non-crosslinked thermoplastic resin layer.

When the non-crosslinked thermoplastic resin layer fuses to a member tobe joined, the interior of said resin layer is melted to expand by theheat supplied from the current carrying electric wire and the pressurein the molten resin layer will increase. When satisfactory conditions offusion are reached, the melt of non-crosslinked thermoplastic resin willcome out of the fine orifice to indicate the point of time at which thefusion was completed. The extruding non-crosslinked thermoplastic resinhas a different color than the surrounding crosslinked thermoplasticresin layer and hence can be readily identified. The crosslinkedthermoplastic resin will not become fluid but remains as a gel even ifit is melted, and only the non-crosslinked thermoplastic resin willbecome fluid and come out of the orifice.

The third embodiment of the present invention is described belowspecifically with reference to FIG. 6, which is a front view of anelectrofusion joint, with its right half shown in cross section,according to an example of the third embodiment. This electrofusionjoint has such a structure that its right half is symmetric to its lefthalf.

Except for the colors of the outer and inner layers and the presence ofa fine orifice, the electrofusion joint shown by 25 in FIG. 6 has thesame construction as the electrofusion joint 10 shown in FIG. 1, so thesame components are identified by like numerals and will not bedescribed in detail.

In the electrofusion joint 25 shown in FIG. 6, the crosslinkedpolyolefin layer has not only a different color than the non-crosslinkedpolyolefin layer 13 but also a small orifice 26 that extends from itsouter surface to a point close to the boundary between said layer 12 andthe non-crosslinked polyolefin layer 13. The orifice 26 is formedsimultaneously with the time when the non-crosslinked polyolefin layer13 is laminated as an integral part of a yet to be cross-linkedpolyolefin layer . The second polyolefin layer is then crosslinked toform the crosslinked polyolefin layer 12.

After fabricating the electrofusion joint 25 in the manner describedabove, members to be joined 15 and 16 such as polyolefin tubes aremounted in such a way that the polyolefin layers 13 will contact themembers 15 and 16. Thereafter, an electric current is applied to theelectric wires 14 through leads from an external power source not shown,the non-crosslinked polyolefin layers 13 will melt and fuse to becomeintegral parts of the members 15 and 16.

When fusion occurs, the non-crosslinked polyolefin layers 13 will bemelted to expand by the heat supplied from the electric wires 14 and thepressure in the melt of non-crosslinked polyolefin layers 13 willincrease. When satisfactory conditions of fusion are reached, the meltof non-crosslinked polyolefin will come out of the fine orifices 26 toindicate the time at which the fusion was completed. The extrudingnon-crosslinked polyolefin has a different color than the crosslinkedpolyolefin layer 12 and hence can be readily identified. The crosslinkedpolyolefin layer 12 will not become fluid but remains as a gel even ifit is melted and only the non-crosslinked thermoplastic resin willbecome fluid. Hence, the point of time at which fusion was completed canbe correctly indicated, allowing the operator to stop the application ofcurrent to the electric wires 14 at the right time.

The electrofusion joints according to the first and second embodimentsof the present invention may be used as the joint of the thirdembodiment as long as the outer crosslinked thermoplastic resin has afine orifice that extends from its outer surface to a point close to theboundary between said crosslinked thermoplastic resin layer and thenon-crosslinked thermoplastic resin layer having a different color. Thejoining portion may be tubular or shaped like a saddle as will bedescribed hereinafter. The other joining portion which is or may befitted with a screw or some other connecting member to establishmechanical coupling to a member to be joined.

As described above in detail, according to the third embodiment of thepresent invention, a crosslinked thermoplastic resin layer has anon-crosslinked thermoplastic resin layer as an integral part that has adifferent color and which has a heating electric wire provided eitherwithin or on the outer or inner surface thereof. Further, saidcrosslinked thermoplastic resin layer has a fine orifice that extendsfrom its outer surface to a point close to the boundary between the tworesin layers. This allows the operator to check in an easy and exact waythe point of time when the fusion of joint was completed, therebyinsuring that members to be joined are completely fused to the joint.Thus, the electrofusion joint according to the third embodiment of thepresent invention will perform satisfactorily at elevated temperaturesas evidenced by high heat resistance and exhibits good sealing property.In addition, the joint can be handled with efficiency in mounting andvarious other operations.

The fourth embodiment of the present invention is described below withreference to FIGS. 7 to 9. The electrofusion joint according to thefourth embodiment is characterized in that at least one of the portionsfor establishing connection to other members of interest in theelectrofusion joint of the first embodiment is a connecting portionhaving a tubular crosslinked thermoplastic resin layer and a connectingmember that is inserted inwardly or outwardly of said crosslinkedthermoplastic resin layer and secured thereto either mechanically by ascrew or some other means or chemically by means of an adhesive materialsuch as a modified thermoplastic resin.

Illustrative connecting members that can be used in the fourthembodiment of the present invention include metal tubes and non-metallictubes such as ceramic tubes and resin tubes having at one end a screw orsome other mechanical means which allow for connection to connectingterminals. Such connecting members are preferably secured to thecrosslinked thermoplastic resin layer by means of an adhesive materialsuch as a modified thermoplastic resin. The adhesive material ispreferably provided between the connecting member and the crosslinkedthermoplastic resin layer. If desired, the adhesive material may bedispersed in the crosslinked thermoplastic resin layer.

Illustrative modified thermoplastic resins that can be used in thefourth embodiment of the present invention are polyolefins that havebeen modified by graft copolymerization with modifying monomersincluding unsaturated carboxylic acids such as acrylic acid and maleicacid, unsaturated carboxylic acid anhydrides such as maleic anhydride,amides of unsaturated carboxylic acids, and unsaturated epoxides such asglycidyl methacrylate. The content of a modifying monomer in themodified thermoplastic resin is desirably within the range of from 0.001to 5 wt % of the modified thermoplastic resin.

The electrofusion joint fitted with a connecting member according to thefourth embodiment of the present invention may be fabricated by thefollowing procedure: at least two components, i.e., the non-crosslinkedthermoplastic resin layer having a heating electric wire provided eitherwithin or on its outer or inner surface and a connecting member having acoating of an adhesive material such as a modified thermoplastic resin,are inserted into an injection mold cavity; a crosslinkablethermoplastic resin is injected and laminated on said non-crosslinkedthermoplastic resin layer and said connecting member to form an integralassembly; thereafter, the crosslinkable thermoplastic resin layer iscrosslinked to form the crosslinked thermoplastic resin layer. Ifdesired, the adhesive material need not be coated on the connectingmember but may be dispersed in the crosslinkable thermoplastic resinwhich is to be injected into the mold cavity.

The thus fabricated electrofusion joint is used in the following manner:the connecting member in the connecting portion is joined to aconnecting terminal such as a nozzle on a conduit header; at the sametime, a member to be joined such as a thermoplastic resin tube ismounted in such a way that it contacts the non-crosslinked thermoplasticresin layer in the joining portion; when an electric current is appliedto the electric wire from an external power source connected by a lead,the non-crosslinked thermoplastic resin layer will melt and fuses to themember of interest to become an integral part of the latter. Byfollowing this procedure, the metallic connecting terminal can beconnected to the resin tube in a leak-free and reliable manner.

The electrofusion joint fitted with a connecting member according to thefourth embodiment of the present invention is described below withreference to the preferred examples depicted in drawings. FIG. 7 is across section of one example of the electrofusion joint fitted with aconnecting member. As shown in this diagram, the electrofusion jointindicated by 30 has the same construction as the electrofusion joint 10shown in FIG. 1 except that the connecting portion on its left side isfitted with a connecting member 33. Hence, the same components areidentified by like numerals and will not be detailed in detail.

The electrofusion joint 30 shown in FIG. 7 has a tubular crosslinkedpolyolefin layer 12, a joining portion comprising a non-crosslinkedpolyolefin layer 13 formed as an integral part of said crosslinkedpolyolefin layer 12 on the inner side of one end thereof at a positionwhere it contacts a member to be joined 15, and a heating electric wire14 provided either within or on the outer or inner surface of saidnon-crosslinked polyolefin layer 13, a connecting member 33 secured tothe other end of said crosslinked polyolefin layer 12 by being insertedinwardly of the same, and a modified polyolefin layer 34 serving as anadhesive material which is provided between the inserted portion 33a ofthe connecting member 33 and the crosslinked polyolefin layer 12. Thecrosslinked polyolefin layer 12 has a tubular structure that surroundsthe entire circumference of the member 15 and the inserted portion 33aof the connecting member 33 in their mating portion 35 and nearby areas.The non-crosslinked polyolefin layer 13 is superposed on the innersurface of the crosslinked polyolefin layer 12 in an area at one endthereof in its longitudinal direction that corresponds to the member 15.The electric wire 14 is buried in the non-crosslinked polyolefin layer13.

The connecting member 33 is a metal tube which has a screw 36 formed asa mechanical connecting portion in a projection 33b on the side oppositeto the inserted portion 33a. A hexagonal flange 37 which is to begripped with a spanner is formed midway between 33a and 33b. Themodified polyolefin layer 34 extends on the entire circumference of thespace between the inserted portion 33a of the connecting member 33 andthe crosslinked polyolefin layer 12 so as to adhere them together.

The electrofusion joint 30 having the construction described above isfabricated by the following procedure: the non-crosslinked polyolefinlayer 13 having the heating electric wire 14 either buried within or inits outer or inner surface or wound around its surface, and the insertedportion 33a of the connecting member 33 coated with the modifiedpolyolefin layer 34 on the outer surface are inserted into an injectionmold cavity; subsequently, a crosslinkable polyolefin containing acrosslinking agent, a crosslinking aid, etc. in a polyolefin is injectedand laminated on the non-crosslinked polyolefin layer 13 and theconnecting member 33 to form an integral assembly; and thereafter saidcrosslinkable polyolefin layer is crosslinked to form the crosslinkedpolyolefin layer 12.

The so fabricated electrofusion joint 30 is connected at one end to aconnecting terminal such as a nozzle on a conduit header by fitting thescrew 36 in the projection 33b of the connecting member 33 into saidterminal. Subsequently, the member to be joined 15 such as a polyolefintube is inserted into the other end of the joint 30 inwardly of thenon-crosslinked polyolefin layer 13 until it contacts the insertedportion 33a of the connecting member 33. Thereafter, an electric currentis applied to the electric wire 14 from an external power sourceconnected by a lead not shown, whereupon the non-crosslinked polyolefinlayer 13 is melted and fuses to become an integral part of the member15.

As in the first embodiment, the electrofusion joint 30 described abovehas the tubular crosslinked polyolefin layer 12 responsible forimparting heat resistance to the joint, and hence it is capable ofretaining its own shape in an effective way even if it is used to joinhot water pipes. Further, the non-crosslinked polyolefin layer 13 whichis an integral part of the crosslinked polyolefin layer 12 together withthe connecting member 33 fuses to the member 15 to become an integralpart thereof. Hence, the joint has good sealing property which ismaintained for a prolonged period even if it is used to join hot waterpipes.

FIGS. 8 and 9 are cross sections showing other examples of theelectrofusion joint according to the fourth embodiment of the presentinvention. In the embodiment shown in FIG. 8, the inserted portion 33aof the connecting member 33 is secured to the crosslinked polyolefinlayer 12 by means of a screw 38. The projection 33b has a flange 33cwhich engages a socket 39 for providing connection to a connectingterminal such as a nozzle.

In the embodiment shown in FIG. 9, the crosslinked polyolefin layer 12is in elbow form and the inserted portion 33a of the connecting member33 is secured to an end of the elbow by means of a screw 38. Theprojection 33b of the connecting member 33 is in socket form which isadapted to connect to a connecting terminal such as a nozzle.

In the embodiments described above, the modified polyolefin layer 34 isformed separately as a layer of adhesive material. If desired, themodified polyolefin may be dispersed in the crosslinked polyolefin layer12. The shapes and structures of the crosslinked polyolefin layer 12 andthe non-crosslinked polyolefin layer 13 are not limited to those shownin FIGS. 7 to 9 and various modifications are possible.

The electrofusion joint fitted with a connecting member according to thefourth embodiment of the present invention is applicable to every shapeand structure of electrofusion joint according to the first embodimentas long as it has plurality of open ends, one of which is provided witha connecting portion having a connecting member secured thereto.

As described above, the electrofusion joint according to the fourthembodiment of the present invention has at least a connecting portionthat has a connecting member secured to a crosslinked thermoplasticresin layer, and at least a joining portion that comprises anon-crosslinked thermoplastic resin layer formed as an integral part ofthe crosslinked thermoplastic resin layer and a heating electric wireprovided either within or in the outer or inner surface of saidnon-crosslinked thermoplastic layer. Hence, this electrofusion jointfitted with a connecting member performs satisfactorily at elevatedtemperatures as evidenced by high heat resistance and exhibits goodsealing property. In addition, this joint can be handled efficiently insuch operations as mounting members to be joined.

The fifth embodiment of the present invention is described below withreference to FIGS. 10 to 12. The electrofusion joint according to thefifth embodiment has at least one electrofusion joining portion providedwith a support of the member to be joined as in the second embodimentand at least one connecting portion having a connecting portion as inthe fourth embodiment. As in the electrofusion joint according to thesecond embodiment, the support of the member to be joined may be formedas an integral part of the crosslinked thermoplastic resin layer or thenon-crosslinked thermoplastic resin layer. Alternatively, the supportmay be formed as an integral part of the connecting member, or it may beformed of other materials. The groove into which the member to be joinedis to be inserted may be formed in such a way that it opens at one endof the electrofusion joint.

The electrofusion joint equipped with a connecting member according tothe fifth embodiment of the present invention can be fabricated by thesame procedure as adopted in the fourth embodiment. The adhesivematerial for adhering the connecting member to the joint need not becoated on the connecting member but may be dispersed in thecrosslinkable thermoplastic resin which is to be injected into the moldcavity. The support of the member to be joined may be preliminarilyformed as an integral part of the connecting member. Alternatively, itmay be formed as an integral part of the crosslinkable thermoplasticresin layer which is to form the crosslinked thermoplastic resin layer.

The fifth embodiment of the present invention is described below withreference to the preferred examples shown in FIGS. 10 to 12, which arecross sections showing three different examples of the electrofusionjoint equipped with a connecting member according to the fifthembodiment.

The electrofusion joints with a connecting member that are indicated by40 and 41 in FIGS. 10 and 11 are the same as the electrofusion jointsshown in FIGS. 4 and 5 except that one end thereof (the left open end asviewed in these drawings) is formed as a connecting portion fitted witha connecting member as on the left end of the electrofusion joint 30shown in FIG. 7. Thus, the same components are identified by likenumerals and will not be described in detail.

The electrofusion joint 40 shown in FIG. 10 has the following essentialcomponents: a tubular crosslinked polyolefin layer 12 forming the mainbody of the joint; an electrofusion joining portion that comprises anon-crosslinked polyolefin layer 13 formed as an integral part of thecrosslinked polyolefin layer 12 on the inner surface at one end (on theright side as viewed in FIG. 10) in the area where it contacts themember to be joined 15, a heating electric wire 14 provided eitherwithin or on the outer or inner surface of said non-crosslinkedpolyolefin layer 13, and a support 23 of the member 15 provided in sucha way as to form a groove 22 inwardly of the non-crosslinked polyolefinlayer 13 into which the member 15 is to be inserted; and a connectingportion that comprises a connecting member 33 secured to the other end(on the left side as viewed in FIG. 10) of the crosslinked polyolefinlayer 12 by being inserted inwardly of the same, and a modifiedpolyolefin layer 34 serving as an adhesive material which is providedbetween the inserted portion 33a of the connecting member 33 and thecrosslinked polyolefin layer 12.

According to the fifth embodiment, the support 23 is formed as anintegral part of the crosslinked polyolefin layer 12 in the exampleshown in FIG. 10 by being made of a crosslinked polyolefin, and it isformed as an integral part of the non-crosslinked polyolefin layer 13 inthe example shown in FIG. 11 by being made of a non-crosslinkedpolyolefin.

In the electrofusion joint 42 fitted with connecting member and which isshown in FIG. 12, the support 23 extends as an integral part of theinserted portion 33a of the connecting member 33 in such a way as toform the groove 22 between said support and the non-crosslinkedpolyolefin layer 13, into which groove the member to be joined is to beinserted.

The electrofusion joint 42 having the construction described above maybe fabricated by the following procedure: the non-crosslinked polyolefinlayer 13 having the heating electric wire 14 either buried within or inits outer or inner surface or wound around its surface, as well as theinserted portion 33a of the connecting member 33 coated with themodified polyolefin layer 34 on the outer surface and the support 23 areinserted into an injection mold cavity; subsequently, a crosslinkablepolyolefin containing a crosslinking agent, a crosslinking aid, etc. ina polyolefin is injected and laminated on the non-crosslinked polyolefinlayer 13, the connecting member 33 and the support 23 to form anintegral assembly; and thereafter said crosslinkable polyolefin layer iscrosslinked to form the crosslinked polyolefin layer 12.

Each of the electrofusion joints 40, 41 and 42 according to the fifthembodiment can be connected to a connecting terminal such as a nozzle ona conduit header by threading the screw 36 in the projection 33b of theconnecting member 33 into said terminal. Subsequently, the member to bejoined 15 such as a polyolefin tube is inserted into the groove 22 andthe non-crosslinked polyolefin layer 13 integral with the crosslinkedpolyolefin layer 12 will thermally melt to fuse to become an integralpart of the member 15. Thus, the joints 40, 41 and 42 according to thefifth embodiment not only have high ability to retain their own shapebut also exhibit good sealing performance which will be maintained for aprolonged period even if they are used to join hot water supply pipes.

As the non-crosslinked polyolefin layer 13 melts, the member 15 which ismade of a thermoplastic resin will soften but will not deform since itsinner surface is supported by the support 23. Thus, the fluid channel ofthe member 15 will not become narrow but maintains a cross-sectionalarea substantially the same as before the member 15 was joined.

As described above, the electrofusion joint fitted with a connectingmember according to the fifth embodiment of the present invention hasboth the joining portion used in the second embodiment and theconnecting portion fitted with a connecting member as in the fourthembodiment. Thus, the joint can be designed according to the variousexamples of these previous embodiments to exhibit the advantages theyattain.

As described in detail on the foregoing pages, the electrofusion jointequipped with a connecting member according to the fifth embodiment ofthe present invention has both a connecting portion to which aconnecting member is secured and a joining portion having anon-crosslinked thermoplastic resin layer furnished with heatingelectric wire and a support of a member to be joined. This joint can beeasily connected to a connecting terminal such as a nozzle on a conduitheader for supplying hot water. Further, the joint will performsatisfactorily at elevated temperatures as evidenced by high heatresistance and exhibits good sealing property. In addition, this jointis capable of joining various members without causing their deformationand it can be handled efficiently in mounting and various otheroperations.

The sixth embodiment of the present invention is described below withreference to FIGS. 13 to 18. The electrofusion joint according to thesixth embodiment has a first connecting portion and a second connectingportion. The first connecting portion is saddle-shaped joining portionhaving the construction described in connection with the firstembodiment, and the second connecting portion is on the top of thissaddle-shaped joining portion.

The second connecting portion may be of any construction. For example,it may have the same construction as the first connecting portion whichis an electrofusion joining portion comprising a crosslinkedthermoplastic resin layer, a non-crosslinked thermoplastic resin layerand a heating electric wire. It may be fitted with a fastening device orsome other connecting member as in the fourth embodiment. Alternatively,a dual structure consisting of a crosslinked thermoplastic resin layerand a non-crosslinked thermoplastic resin layer may be coupled toanother electrofusion joint.

The electrofusion joint according to the sixth embodiment of the presentinvention can be fabricated by the following procedure: to begin with,as in the first embodiment, a non-crosslinked thermoplastic resin layershaped like a saddle which has a heating electric wire buried eitherwithin or in its outer or inner surface is positioned in a mold cavity,and a crosslinkable thermoplastic resin layer is injected and laminatedin saddle form over the non-crosslinked thermoplastic resin layer, andsubsequently crosslinked to form the cross-linked thermoplastic resinlayer; the resulting joining portion is used as the first connectingportion; thereafter, the second connecting portion is formed as anintegral part on the top of the saddle-shaped crosslinked thermoplasticresin layer in the first connecting member.

The thus fabricated electrofusion joint is used in the following manner:the first connecting portion is mounted on the lateral side of a memberto be joined such as a tube having a thermoplastic resin layer in such away that the non-crosslinked thermoplastic resin layer will contact saidmember to be joined; then, as in the first embodiment, an electriccurrent is applied to the heating electric wire, whereupon thenon-crosslinked thermoplastic resin layer will melt and fuse to themember of interest as an integral part thereof.

Subsequently, the connecting terminal of another member to be joined isconnected to the second connecting portion formed on the top of thefirst connecting portion, and this enables the second member to beconnected to any desired part of the lateral side of the first member.

The second connecting portion of the electrofusion joint may be formedby repeating the procedure of fabricating a joining portion as describedin connection with the first embodiment and the fabricated joiningportion can be fused as an integral part of a member to be joined suchas a tube having a thermoplastic resin layer.

The second connecting portion having a connecting member as in thefourth embodiment may be obtained by shaping a non-crosslinkedthermoplastic resin layer together with connecting member positioned ina mold cavity. The connecting member can be securely adhered to thisconnecting member if shaping is performed with an adhesive material suchas a modified thermoplastic resin being coated in the area where theconnecting member is buried. The second connecting portion thus obtainedmay be connected to the connecting terminal of another member to bejoined by making use of mechanical connecting means such as a screw or acoupler.

The second connecting portion of a dual structure may be obtained bymolding a non-crosslinked thermoplastic resin layer on the circumferenceof a crosslinked thermoplastic resin layer as an integral part thereofby repeating the procedure described above. The resulting connectingportion has a fusible non-crosslinked thermoplastic resin layer on itscircumference. This second connecting portion can be connected toanother member to be joined by bringing it into end-to-end relationshipwith the connecting terminal of this member and covering the entirecircumference of the mating portion and nearby areas with anotherelectrofusion joint.

Specific examples of the sixth embodiment of the present invention arehereunder described with reference to FIGS. 13 to 18. FIG. 13 is a frontview of an electrofusion joint according to an example of the sixthembodiment. FIG. 14 is a cross section taken on line A--A of FIG. 13.FIG. 15 is a bottom view of the joint shown in FIG. 13. FIG. 16 is across section taken on line B--B of FIG. 14 and show how the joint ismounted on a member to be joined. The electrofusion joint generallyindicated by 50 has the first connecting portion 51a formed at one endas a saddle-shaped joining portion and the second connecting portion 51bintegral with the first connecting portion 51a which is formed as atubular joining portion in the center of the top of 51a. The firstconnecting portion 51a has a crosslinked polyolefin layer 12a in saddleshaped having an opening 52 in the central area, a non-crosslinkedpolyolefin layer 13a in saddle shaped formed as an integral part of thecrosslinked polyolefin layer 12a on the inner surface thereof at theposition where it contacts a member to be joined 15a, and a heatingelectric wire 14a provided within the non-crosslinked polyolefin layer13a in saddle shape.

The second connecting portion 51b has a tubular crosslinked polyolefinlayer 12b formed as an integral part of the crosslinked polyolefin layer12a, a tubular non-crosslinked polyolefin layer 13b formed as anintegral part of the crosslinked polyolefin layer 12b on the innersurface thereof at the position where it contacts another member to bejoined 15b, and a heating electric wire 14b provided within thenon-crosslinked polyolefin layer 13b.

Each of the members 15a and 15b is a pipe having a layer ofthermoplastic resin such as polyethylene. While they may be totally madeof a fusible thermoplastic resin, those which are made of heat-resistantmaterials such as crosslinked polyolefins should be coated with fusiblethermoplastic resin on their outer surface. The member 15a has a bypasshole 53 in its lateral side on a position that corresponds to theopening 52.

The electrofusion joint 50 having the construction described above canbe fabricated by the following procedure: non-crosslinked polyolefinlayers 13a and 13b having heating electric wires 14a and 14b buriedtherein are inserted into a mold cavity; a crosslinkable polyolefincontaining a crosslinking agent, a crosslinking aid, a catalyst, etc. ina polyolefin is injected and laminated on the non-crosslinked polyolefinlayers 13a and 13b to form an integral assembly; thereafter, thecrosslinkable polyolefin layer is crosslinked to form crosslinkedpolyolefin layers 12a and 12b.

The thus fabricated electrofusion joint 50 is used in the followingmanner: it is first mounted in such a way that the non-crosslinkedpolyolefin layer 13a in saddle shape will contact the lateral side ofthe member 15a such as a polyolefin tube; when an electric current isapplied to the electric wire 14a, the non-crosslinked polyolefin layer13a will melt and fuse to become an integral part of member 15a. Afterthe melting and fusing, the bypass hole 53 is formed on the lateral sideof the member 15a, which is positioned corresponding to the opening 52,using a tool for making a hole.

Subsequently, the end of the other member to be joined 15b is insertedinto the second connecting portion 51b until it contacts thenon-crosslinked polyolefin layer 13b; when an electric current isapplied to the electric wire 14b, the non-crosslinked polyolefin layer13b will fuse to become an integral part of member 15b. Thus, twomembers 15a and 15b will connect to each other via the bypass hole 53and the opening 52.

In the electrofusion joint 50 described above, the crosslinkedpolyolefin layers 12a and 12b forming the main body of the joint areresponsible for imparting heat resistance to the joint. Hence, the jointis capable of retaining its own shape in an effective way even if it isused to join hot water supply pipes. Further, the non-crosslinkedpolyolefin layers 13a and 13b which are integral parts of thecrosslinked polyolefin layers 12a and 12b, respectively, will fuse tothe members 15a and 15b to become integral parts thereof. Hence, thejoint has good sealing property which is maintained for a prolongedperiod even if it is used to join hot water pipes.

FIGS. 17 and 18 show other examples of the sixth embodiment and they areequivalent to cross sections taken on line B--B of FIG. 14. In each ofthe electrofusion joints indicated by 55 and 56, the first connectingportion 51a is composed of a joining portion that is shaped like asaddle as in the example shown in FIGS. 13 to 16.

In the electrofusion joint 55 shown in FIG. 17, the second connectingportion 51b is such that the inserted portion 33a of a connecting member33 is securely adhered by means of an adhesive layer 34 such as amodified polyolefin layer to the tubular crosslinked polyolefin layer12b shaped as an integral part of the crosslinked polyolefin layer 12a.The connecting member 33 is a metal tube which has on its projection 33ba screw or some other means 36 by which it is joined to member 15b. Ahexagonal flange 37 which is to be gripped with a spanner is formedmidway between 33a and 33b.

With the connecting member 33 inserted into an injection mold cavity asin the fourth embodiment, the electrofusion joint 55 having theconstruction described above is fabricated by the procedure alreadydescribed in connection with the fourth embodiment. The first connectingportion 51a is connected to member 15a in the manner already described.The second connecting portion 51b is joined to the other member 15b bythe joining means 36. The joining means 36 by which the connectingmember 33 is joined to member 15b may assume another form such as asocket having a female screw.

In the example shown in FIG. 18, the second connecting portion 51b mayconsist of a crosslinked polyolefin layer 12a, a tubular crosslinkedpolyolefin layer 12b formed as an integral part thereof, and a tubularnon-crosslinked polyolefin layer 13b laminated on the circumference oflayer 12b as an integral part thereof.

The electrofusion joint 56 having the construction described above isfabricated by the procedure already described, with the non-crosslinkedpolyolefin layer 13b being shaped by lamination over the tubularcrosslinked polyolefin layer 12b as an integral part thereof. The secondconnecting portion 51b may be connected to the member 15b by means ofanother electrofusion joint. Alternatively, it may be directly connectedto a member constructed as an electrofusion joint.

The construction of the second connecting portion 51b described above isnot limited to those shown in FIGS. 13 to 18. The heating electric wires14a and 14b may be provided on either the outer or inner surface of thenon-crosslinked polyolefin layers 13a and 13b.

As described in detail on the foregoing pages, the electrofusion jointaccording to the sixth embodiment of the present invention has a joiningportion comprising a crosslinked thermoplastic resin layer in saddleform, a non-crosslinked thermoplastic resin layer formed as an integralpart of said crosslinked thermoplastic resin layer, and a heatingelectric wire provided either within or on the outer or inner surface ofsaid non-crosslinked thermoplastic resin layer. Hence, this jointenables one member to be fused to the lateral side of another memberwhile performing satisfactorily at elevated temperatures as evidenced byhigh heat resistance and exhibiting good sealing property. In addition,this joint can be handled efficiently in mounting and various otheroperations.

The seventh embodiment of the present invention is described below withreference to FIGS. 19 and 20. This embodiment provides a header fordistributing hot water from a heat source providing apparatus. Theheader comprises a header body shaped of a crosslinked thermoplasticresin in a hollow form, a receptacle provided on the inlet side of saidheader body and at least one receptacle on the outlet side, at leastpart of which receptacles is an electrofusion joining portion of thesame type as used in the first embodiment which comprises a crosslinkedthermoplastic resin and a non-crosslinked thermoplastic resin having aheating electric wire provided either within or on its outer or innersurface.

When the non-crosslinked thermoplastic resin layer and the heatingelectric wire are to be formed at one or more receptacles, the otherreceptacles may be fitted with connecting member commonly used toestablish connection to pipes. An illustrative connecting member is ametal tube having at one end a screw or some other means forestablishing coupling to connecting terminals. The connecting member ispreferably secured to the crosslinked thermoplastic resin layer by meansof bonding with an adhesive material such as a modified thermoplasticresin. The adhesive material is preferably interposed between theconnecting member and the crosslinked thermoplastic resin layer but ifdesired, it may be dispersed in the crosslinked thermoplastic resinlayer.

The header according to the seventh embodiment of the present inventionis fabricated by the following procedure: a tubular non-crosslinkedthermoplastic resin layer having a heating electric wire provided eitherwithin or on its outer or inner surface is inserted into an injectionmold cavity; a crosslinkable thermoplastic resin is injected andlaminated on the non-crosslinked thermoplastic resin layer to form anintegral unit; thereafter, the crosslinkable thermoplastic resin layeris crosslinked to form the crosslinked thermoplastic resin layer. If aconnecting member is necessary, it may be attached to the completedheader. Alternatively, it may be injection molded together with theother components, with it being inserted into the mold cavity after itwas coated with an adhesive material such as a modified thermoplasticresin. In this latter case, the adhesive material need not be coated onthe non-crosslinked thermoplastic resin layer but may be dispersed inthe crosslinkable thermoplastic resin to be injected.

The so fabricated header is used with the water supply main from theheat source providing apparatus being connected to the receptacle on theinlet side and branch pipes to the necessary faucets being connected tothe receptacles on the outlet side. In the case where a connectingmember is used, the header is installed in such a way that theconnecting member is connected to the connecting terminal of a member tobe joined (i.e., a pipe) whereas a plastic pipe such as a thermoplastictube is brought into contact with the non-crosslinked thermoplasticlayer. When an electric current is applied to the heating electric wire,the non-crosslinked thermoplastic resin will melt and fuse to become anintegral part of the plastic pipe. This enables the header to beconnected to all pipes in a leak-free and reliable manner.

As in the case of members to be joined by the electrofusion jointsdescribed on the foregoing pages, pipes to be connected to the headerare preferable such that the surface layer or the entire portion is madeof a thermoplastic resin, in particular, a miscible thermoplastic resin.Pipes made of non-crosslinked thermoplastic resins such as polyolefinswill exhibit particularly good fusing ability.

The header for supplying hot water according to the seventh embodimentof the present invention is described below in a specific way bereference to the preferred examples shown in FIGS. 19 and 20, which arepartial fragmentary front views of two different examples of the header.

The header generally indicated by 60 is composed of a hollow header body61 and a crosslinked polyolefin layer 62 forming a tubular receptacle 91on the inlet side and a plurality of tubular receptacles 92a, 92b, 92cand 92d on the outlet side. The header body and the receptacles areshaped of a crosslinked polyolefin into an integral unit. The receptacle91 on the inlet side is open at one end of the header 60 whereas thereceptacles 92a, . . . on the outlet side which are arranged in a roware open in a direction perpendicular to the receptacle 91.

All receptacles 91, 92a, 92b, 92c and 92d (in the example shown in FIG.19) or receptacles on the outlet side 92a-92d (in the example shown inFIG. 20) have the following construction: on the inner surface of thetubular crosslinked polyolefin layer 62 shaped as an integral part ofthe header body 61, a tubular non-crosslinked polyolefin layer 63 islaminated to become an integral part of the crosslinked polyolefin layer62, and a coil of heating electric wire 64 is buried within thenon-crosslinked polyolefin layer 63 and connected to terminals 65 and 66to form an electrofusion joining portion of the same type as describedin connection with the first embodiment. A connecting member 33 isattached to the receptacle 91 on the inlet side of the header shown inFIG. 20.

The connecting member 33 is a metal tube which has a screw 36 formed onthe projection 33b on the side opposite to the inserted portion 33a toserve as connecting means. A hexagonal flange 37 which is to be grippedwith a spanner is formed midway between 33a and 33b. A modifiedpolyolefin layer 34 is disposed along the entire circumference of thespace between the inserted portion 33a of the connecting member 33 andthe crosslinked polyolefin layer 62 to adhere them together.

The header 60 having the construction described above is fabricated bythe following procedure: the non-crosslinked polyolefin layer 63 havingthe heating electric wire 64 either buried within or on its outer orinner surface or wound around its surface is inserted into an injectionmold cavity; a crosslinkable polyolefin containing a crosslinking agent,a crosslinking aid, etc. in a polyolefin is injected and laminated overthe non-crosslinked polyolefin layer 63 to form an integral unit;thereafter, the crosslinkable polyolefin layer is crosslinked to formthe crosslinked polyolefin layer 62. The connecting member 33 may beeither attached to the completed header or injection molded togetherwith the other components, with the inserted portion 33a of theconnecting member 33 being inserted into the mold cavity after it wascoated with the modified polyolefin layer 34 on the outer surface.

The thus fabricated header 60 is used in such a way that the water main88 from the heat source providing apparatus 82 (see FIG. 23) isconnected to the receptacle 91 on the inlet side whereas branch pipes93a, 93b, 93c and 93d to faucets 83, 84, 85, etc. are connected to thereceptacles 92a, 92b, 92c and 92d, respectively, on the outlet side. Ifthe header is fitted with the connecting member 33 as shown in FIG. 20,said member is connected to the connecting terminal of the water main 88whereas branch pipes 93a, 93b, 93c and 93d which are made of plasticsuch as polyolefins are mounted in such as way that they contact thenon-crosslinked polyolefin layer 63 in receptacles 92a, 92b, 92c and 92das shown in FIG. 23. In the example shown in FIG. 19, both the watermain 88 and branch pipes 93a, 93b, 93c and 93d are connected to thereceptacle 91, 92a, 92b, 92c and 92d in such a way that they contact thenon-crosslinked polyolefin layer 63 in these receptacles as shown inFIG. 23. Thereafter, an electric current is applied to the electric wire64 via terminals 65 and 66, whereupon the non-crosslinked polyolefinlayer 63 will melt and fuse to become an integral part of each pipe tobe connected. This insures that the header 60 is positively connected tothe necessary pipes in a leak-free way.

The connecting member 33 is suitable for establishing connection tometal pipes whereas the electrofusion joint is suitable when a plasticpipe is to be connected. Thus, the layout of these devices can bedetermined in accordance with the specific pipe to be joined.

The header 60 has the crosslinked polyolefin layer 62 as a memberresponsible for imparting heat resistance, so it is capable of retainingits own shape effectively even if it is used to join hot water pipes.Further, the non-crosslinked polyolefin layer 63 has fused to become anintegral part of the crosslinked polyolefin layer 62 together with theconnecting member 33, so the header will exhibit good sealing propertywhich is maintained for a prolonged period even if it is used to joinhot water pipes.

In the example shown in FIG. 20, the connecting member 33 is fitted tothe receptacle 91 on the inlet side but it may be attached to one ormore of the receptacles on the outlet side. The connecting member 33 mayhave connecting means other than screws.

As described on the foregoing pages, the header according to the seventhembodiment of the present invention has an electrofusion joining portionthat comprises a non-crosslinked thermoplastic resin layer and a heatingelectric wire and that is fitted to at least one of the receptacles onthe header body made of a crosslinked thermoplastic resin. Because ofthis arrangement, the header has high heat resistance, exhibits goodsealing performance, is lightweight and resistant to corrosion, can beeasily connected to plastic pipes, and is suitable for large-scaleproduction.

The eighth embodiment of the present invention is described below withreference to FIGS. 21 and 22. The header for supplying hot wateraccording to the present invention comprises a header body shaped of acrosslinked thermoplastic resin in hollow form and a plurality ofreceptacles on the outlet side of the header body which are formed of acrosslinked thermoplastic resin as an integral part of said header bodyin such a way that said tubular resin layer has a bore diametersufficient to admit the flow rate of hot water distributed to eachreceptacle.

Preferably, the receptacle on the inlet side and the plurality ofreceptacles on the outlet side are each made of a laminate of thetubular crosslinked thermoplastic resin layer and a tubularnon-crosslinked thermoplastic resin layer that is capable of joining byfusion. More preferably, each of these receptacles is an electrofusionjoining portion that has a heating electric wire provided either withinor on its outer or inner surface as in the first embodiment.

In fabricating the header according to the eighth embodiment, aninjection mold must be employed whose cavity configuration is such thata plurality of receptacles having different bore diameters can be moldedon the outlet side. Lamination of a non-crosslinked thermoplastic resinlayer on a receptacle, placement of a heating electric wire and fixationof a connecting member can be performed in entirely the same manner asin the seventh embodiment and will not be described in detail.

The so fabricated header is used with the water supply main from theheat source providing apparatus being connected to the receptacle on theinlet side and branch pipes to the necessary faucets being connected tothe receptacles on the outlet side. The receptacles on the outlet sidehaving different bore diameters are connected to branches having thecorresponding bore diameters. In the case where a connecting member isattached to a receptacle, it is couples to the connecting terminal ofthe pipe to which said receptacle is to be connected. In the case wherea non-crosslinked thermoplastic resin layer is laminated on areceptacle, a plastic pipe such as a thermoplastic resin tube is mountedin such a way that it contacts the non-crosslinked thermoplastic resinlayer and thereafter connected by some other means such as anelectrofusion joint. If both a non-crosslinked thermoplastic resin layerand a heating electric wire are to be provided on a receptacle, the pipeto be connected is mounted in the same way and a current is applied tothe electric wire, whereupon the non-crosslinked thermoplastic resinlayer will melt and fuse as an integral part of the pipe. Thus, eithermethod insures that the header is positively connected to the necessarypipe in a leak-free way.

Two different examples of the header according to the eighth embodimentof the present invention are shown in FIGS. 21 and 22. The headers shownin these drawings are identical to those shown in FIGS. 19 and 20,respectively, according to the seventh embodiment except that thereceptacles on the outlet side of the header body have different borediameters, so the same components are identified by like numerals andwill not be described in detail.

In the header generally indicated by 70 in FIGS. 21 and 22, thereceptacle 91 on the inlet side open at one end of the header whereasthe receptacles 92a, 92b, 92c and 92d on the outlet side which arearranged in a row are open in a direction perpendicular to thereceptacle 91 and have different bore diameters Da, Db, Dc and Dd thatare sufficient to admit the flow rate of hot water distributed to eachreceptacle.

The header 70 having the construction described above is used with thewater main 88 from the heat source providing apparatus 82 beingconnected to the receptacle 91 on the inlet side and with differentlysized branch pipes 93a, 93b, 93c and 93d to faucets 83, 84, 85, etc.being connected to receptacles 92a, 92b, 92c and 92d on the outlet sidewhich have bore diameters corresponding to those of the associatedbranch pipes. If the header is fitted with the connecting member 33 asshown in FIG. 22, said member is connected to the connecting terminal ofthe water main 88 whereas branch pipes 93a, 93b, 93c and 93d which aremade of plastics such as polyolefins are mounted in such a way that theycontact the non-crosslinked polyolefin layer 63 in receptacles 92a, 92b,92c and 92d as shown in FIG. 23. In the example shown in FIG. 21, boththe water main 88 and branch pipes 93a, 93b, 93c and 93d are connectedto the receptacles 91, 92a, 92b, 92c and 92d in such a way that theycontact the non-crosslinked polyolefin layer 63 in these receptacles asshown in FIG. 23. Thereafter, an electric current is applied to theelectric wire 64 via terminals 65 and 66, whereupon the non-crosslinkedpolyolefin layer 63 will melt and fuse to become an integral part ofeach pipe to be connected. This insures that the header 70 is positivelyconnected to the necessary pipes in a leak-free way.

The header 70 has the crosslinked polyolefin layer 62 as a memberresponsible for imparting heat resistance, so it is capable of retainingits own shape effectively even if it is used to join hot water pipes.Further, the receptacles 92a, . . . on the outlet side of the headerbody have different bore diameters that are sufficient to admit the flowrate of hot water distributed to each receptacle, so they can bedirectly connected to branch pipes of different bore diameters withoutusing reducers. Thus, the header insures effective sealing and highoperational efficiency. In addition, the non-crosslinked polyolefinlayer 63 has fused to become an integral part of the crosslinkedpolyolefin layer 62 together with the connecting member 33, so theheader will exhibit good sealing property which is maintained for aprolonged period even if it is used to join hot water pipes.

In accordance with the eighth embodiment of the present invention, aheader body and receptacles on its outlet side having different borediameters are shaped as an integral unit by molding of a crosslinkedthermoplastic resin. Thus, the resulting header has high heatresistance, is lightweight and resistant to corrosion, can be easilyconnected to plastic pipes having different bore diameters, and issuitable for large-scale production.

If a non-crosslinked thermoplastic resin layer and even a heatingelectric wire are provided at the receptacle on the inlet side or theplurality of receptacles on the outlet side, a header can be obtainedthat exhibits high sealing performance, particularly for a prolongedperiod, and that allows for easy connection to pipes.

EXAMPLES

The present invention is hereunder described in greater detail withreference to the following examples.

EXAMPLE 1

A medium density polyethylene colored by using a coloring agent was usedas the non crosslinked thermoplastic resin 13 of the present invention.The colored medium density polyethylene crosslinked by using 1.5% byweight of a crosslinking agent (vinyl trimethoxysilane) was used as thecrosslinked thermoplastic resin 12 of the present invention. A Ni Cralloy wire (0.3 mm φ) was used as the material of the heating electricwire 14.

The electrofusion joint 20 having a structure as shown in FIG. 4, towhich the tubes 15 and 16 to be connected having an adaptable caliber of8 to 21.5 mm can be joined, was fabricated in accordance with the abovedescribed methods.

The tubes 15 and 16 to be connected, which were made of the samematerials and have an adaptable caliber, were inserted at one end intogrooves on opposite sides of the electrofusion joint 20. Thereafter, anelectric current was applied to the above described heating electricwires 14 which have been connected to an external electric power forabout 20 seconds by controlling the voltage in order to give anappropriate energy density. For example, conditions for the applicationof electric current in the case of an adaptable caliber (outer diameter)of the tubes being 13 mm were as follows: resistance of the heatingelectric wire 14, 14.5 Ω; voltage, 40 V; and the application time, 20seconds.

When sealing properties of the joining portion were checked aftercompletion of the connection, no leakage was found for at least 100hours under a pressure of 10 kg/cm² at 90° C., which confirmed similarsealing properties of the joint to those of the pipes to be connected.It waa confirmed also that the joint can be handled more efficiently inmounting and other various operations than in the case of joining usingwrenches and the like.

EXAMPLE 2

A modified polyethylene 34 was prepared as the adhesive material for usein the connecting member 33 made of brass, by performing graftcopolymerization of a medium density polyethylene and maleic acid bymeans of a melt kneading. Using the modified polyethylene thus preparedand the same resin materials and electric heating wire materials asdescribed in Example 1, the electrofusion joint 40 equipped with theconnecting member having the structure as shown in FIG. 10 wherein theadaptable caliber of the pipe 15 to be connected is 8 to 21.5 mm wasfabricated in accordance with the above described methods.

The pipe 15 to be connected made of the same material having anadaptable caliber was inserted into the joint, and the joining portionwas connected by applying electric current to the above describedelectric heating wires 14 in the same manner as described in Example 1.

When sealing properties of the joining portion were checked aftercompletion of the connection, it was confirmed that the joint hadsimilar sealing properties to those of the pipes to be connected as theresults described in Example 1. It was also confirmed that the joint canbe handled more efficiently in mounting and other various operationsthan in the case of joining using wrenches and the like as described inExample 1.

What is claimed is:
 1. An electrofusion joint comprisinga main bodyportion comprised of a crosslinked thermoplastic resin, said main bodyportion having an interior surface and an exterior surface; at least onejoining portion comprising a non-crosslinkable thermoplastic resinembedded in the interior surface of said main body portion withoutextending to the extreme end of the electrofusion joint, said joiningportion having an electrical heating wire associated in contacttherewith so that the joining portion may be heat-welded to a pipebrought into contact with said joining portion; and a supporting portionmolded as one piece member with said main body portion of the joint andcomprising the crosslinked thermoplastic resin, a groove into which thepipe is to be inserted being defined between the supporting portion andthe interior surface of said main body portion wherein the joiningportion is embedded.
 2. The electrofusion joint of claim 1, wherein saidmain body portion has a tubular configuration at the end opposite tosaid end provided with said joining portion; and said electrofusionjoint further comprises a connecting member fitted into and fixedlysecured to said tubular end of the main body portion on its interior byan intervening layer comprising a modified thermoplastic resin, saidconnecting member being provided with a mechanically connecting means.3. The electrofusion joint according to claim 1, wherein said electricalheating wire is embedded within said joining portion.
 4. Theelectrofusion joint according to claim 1, wherein said crosslinkedthermoplastic resin constituting said main body portion has a colordifferent from that of said non-crosslinkable thermoplastic resinconstituting said joining portion embedded in the interior surface ofsaid main body portion; and said main body portion has an orificeextending from the exterior surface of said main body to a point in thevicinity of the boundary between the main body portion and the joiningportion, such that, upon heating of the joining portion, a portion ofthe softened non-crosslinkable thermoplastic resin of the joiningportion is urged by the pressure produced by the heating to rise withinsaid orifice to enable the state of the joining portion to be estimatedby visual inspection from the exterior of the main body.
 5. Anelectrofusion joint comprisinga main body portion comprised of acrosslinked thermoplastic resin, said main body portion having aninterior surface and an exterior surface; at least one joining portioncomprising a non-crosslinkable thermoplastic resin embedded in theinterior surface of said main body portion without extending t theextreme end of the electrofusion joint, said joining portion having anelectrical heating wire associated in contact therewith so that thejoining portion may be heat-welded to a pipe brought into contact withsaid joining portion; and a supporting portion molded as one piecemember with said joining portion and comprising the non-crosslinkablethermoplastic resin, a groove into which the pipe is to be insertedbeing defined between the supporting portion and the interior surface ofsaid main body portion wherein the joining portion is embedded.
 6. Theelectrofusion joint according to claim 5, wherein said main body portionhas a tubular configuration at the end opposite to said end providedwith said joining portion; and said electrofusion joint furthercomprises a connecting member fitted into and fixedly secured to saidtubular end of the main body portion on its interior by an interveninglayer comprising a modified thermoplastic resin, said connecting memberbeing provided with a mechanically connecting means.
 7. Theelectrofusion joint according to claim 5 or claim 6, wherein saidelectrical heating wire is embedded within said joining portion.
 8. Anelectrofusion joint comprisinga main body portion comprising acrosslinked thermoplastic resin having a tubular configuration at oneend, said main body portion having an interior surface and an exteriorsurface; at least one joining portion comprising a non-crosslinkablethermoplastic resin embedded in the interior surface of said main bodyportion at an end opposite to the end having a tubular configurationwithout extending to the extreme end of the electrofusion joint, saidjoining portion having an electrical heating wire associated in contacttherewith so that the joining portion may be heat-welded to a pipebrought into contact with said joining portion; a supporting portion, agroove into which a pipe is to be inserted being defined between thesupporting portion and the interior surface of said main body portionwherein the joining portion is embedded; and a connecting member fittedinto and fixedly secured to said tubular end of the main body portion onits interior by an intervening layer comprising a modified thermoplasticresin, said connecting member being provided with a mechanicallyconnecting means, said connecting portion being molded as one piecemember with said supporting portion.
 9. The electrofusion jointaccording to claim 8, wherein said electrical heating wire is embeddedwithin said joining portion.
 10. The electrofusion joint of any one ofclaims 1, 5, or 8, wherein said crosslinked thermoplastic resincomprises a crosslinked polyolefin; and said non-crosslinkablethermoplastic resin comprises a non-crosslinkable polyolefin resin.